Neil Shenvi - Apologetics

Quantum mechanics and materialism

"For my thoughts are not your thoughts, neither are your ways my ways," declares the Lord. "As the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts." -Isaiah 55:8-9

"Great is the Lord and most worthy of praise; his greatness no one can fathom." - Psalm 145:3

"I think it's safe to say that no one understands quantum mechanics." -Richard Feynman

The purpose of this essay is to set forth some of the philosophical implications of quantum mechanics. Quantum mechanics replaced classical mechanics as the reigning theory of physical phenomena in the early 20th century. Today, after decades of testing, thousands of experiments have confirmed the predictions of quantum theory so that it is widely accepted by the scientific community. Yet in my opinion, there is no theory that so fundamentally challenges our intuitive views of reality. The physicists who developed quantum theory in the early 20th century were astonished, shocked, and bewildered by its philosophical implications, to the extent that many of them including Einstein were convinced that it must somehow be wrong (this disagreement is the origin of Einstein's famous comment: 'God doesn't play dice with the universe'). Why this progression from cataclysmic shock to lukewarm complacence? I'm not sure. Certainly, all of the modern textbooks that I have seen have resolutely avoided any discussion of the meaning of quantum mechanics. Furthermore, most of the physicists, non-physicists, atheists and Christians that I've talked to are mostly unaware of the startling issues raised by quantum mechanics. My hope is that this essay will help people understand the significance that quantum theory has for various worldviews, especially materialism.

First, we should note that when it comes to science, and especially when it comes to quantum mechanics, it is important to distinguish between what is fact and what is interpretation. To some extent, it will also be difficult to convey the technical reasons why certain interpretations are unlikely, while others are more widely accepted. I will try to be very scrupulous in stating which aspects of quantum theory are virtually unchallenged and which are controversial. Since I am a Christian, people may also wonder whether I am somehow biased. No doubt I am! But I will try to be as objective as possible and be very clear when an assertion is my opinion rather than a well-established fact.

To begin, let's consider a few assertions of the traditional materialistic worldview. Of course, materialists who are aware of quantum mechanics may have slightly different views, but I suspect that these assertions will resonate with many modern materialists:

1. The laws of physics state that miracles are impossible. For instance, Jesus could not have turned water into wine because that would have violated numerous physical laws (conservation of energy, conservation of mass, the 2nd law of thermodynamics, etc...)

2. Even if God exists, He could not be a God who intervenes in the natural world because he would have to violate the physical laws that he supposedly created.

3. Consciousness or subjective mental experiences are a collective property of brains (just as wetness is a collective property of water molecules). There is no such thing as a "mind" or "consciousness" separate from physical constituents.

4. The universe does not contain "hidden" or "unknowable" realities that are fundamentally inaccessible to science and reason.

There are of course other major components of a materialist worldview, but I think that most materialists would generally agree with these four statements. By the end of this essay I hope to show you that, if you believe quantum mechanics, assertions 1 and 2 and 4 are simply false. Statement 3 can still be retained, but only at an extremely high cost. Based on these statements, I think it is clear what motivated Danish physicist and father of quantum mechanics Niels Bohr to remark "Anyone who is not shocked by quantum mechanics has not understood it."

Quantum mechanics and physical laws

In the days of classical (or Newtonian) mechanics, it was fairly easy for physicists to define what they meant by a physical law. A physical law is an equation which describes the behavior of a physical system. Specifically, in classical mechanics, the motion of particles is described by Newton's equations of motion (F = m * A). Newton's equations of motion are deterministic, meaning that if I know the initial positions and velocities of every particle in my system at some initial time, then I can tell you the precise position and velocity of every particle at any instant in the future with one hundred percent certainty. Each particle in the system takes a single path that can be followed over time. Philosophers in the 18th and 19th centuries quickly decided that such a conception of natural laws had several important consequences. First, if we truly believe that the physical laws are inviolable, then miracles are impossible. For instance, the cells in a dead body begin inevitably to degrade and decompose. For Jesus to have risen from the dead would mean that those cells somehow reversed their decomposition, violating numerous physical laws. Ergo, miracles like the resurrection are impossible. Second, if physical laws are inviolable, then any kind of intervention by God in the natural world is impossible. God cannot answer prayer, because to do so would violate the deterministic evolution of the universe. Thus, we are left with at most a deist view of God as a clockmaker who sets the world ticking, but then is powerless or unwilling to change its course. Finally, if God did choose to intervene in the world, He could only do so by "clumsily" breaking or setting aside the natural laws that He himself created.

Though I disagree with all of these conclusions, I admit that they do fit fairly naturally into a classical mechanical framework. The reasoning is not perfect, but it is fairly compelling. A classical universe certainly seems to fit into a deist conception of God as a distant artisan more than a biblical conception of God as an intimate, personal creator and sustainer. The real problem with these arguments is not their internal consistency, but their dependence on a classical conception of the universe, which has since been overturned.

According to quantum mechanics, the motion of particles is governed by the Schrodinger equation rather than Newton's equations (technically, we should use the Dirac equation, but I'll stick to nonrelativistic quantum mechanics, since that is my area of expertise). In quantum mechanics, the state of a system is determined not by specifying the positions and velocities of every particle in the system, but by the system's wavefunction. In one sense, the Schrodinger equation is also deterministic, because if we know the initial wavefunction of a given system, we can predict the system's wavefunction at any future instant of time. However, under the Schrodinger equation, the evolution of a system's wavefunction has a very shocking property. A particle described by quantum mechanics takes all possible paths. What do I mean by all possible paths? Let me give you an illustration. Let's say I "put" (technically "localize") a particle on one side of a barrier. The barrier is so high that the particle doesn't have nearly enough energy to climb over the barrier. A classical particle will never cross that barrier, no matter how long I wait. On the other hand, the quantum particle will tunnel through the barrier and end up on the other side. This process is well known and is the basis for the tunneling electron microscope. However, what are the implications of this fact?

Let's say I take a rock and put it on my desk. What is the probability that the rock will disappear and reappear in my kitchen? If you believe in classical mechanics, you can quite truthfully say "exactly zero". But if you believe in quantum mechanics, you can only say "it's extraordinarily improbable". Again, let's go a bit further. According to the Feynman path integral formulation of quantum mechanics, if I localize a particle in some region of space at one instant, it has a finite, non-zero probability of ending up anywhere else in the universe (technically, within its light cone) at the next instant of time. So why don't we see rocks teleporting through apartments? Well, like I said, the probability is extraordinarily low. But there is a world of difference philosophically speaking between improbable and impossible. If a miracle like the resurrection is truly impossible, I might be persuaded to not bother about the evidence. But if it is merely improbable, examining the evidence is the only real way to know whether it happened.

So where does quantum mechanics leave us with regard to physical laws? Certainly with a feeling of vague discomfort. A physicist who is being honest with you will have to admit that the most iron-clad laws of physics now no longer deal with certainties, but only probabilities. We have to conclude that miracles are not impossible. Furthermore, when and if God chooses to intervene in the natural world, he can do so without in any way violating the laws of nature as we currently understand them. Lest you think I am exaggerating, let me close this section with a quote from physicist Alvaro de Rujula of Cern who was in charge of writing a safety report for the recently constructed Large Hadron Collider. When asked whether there was a possibility that the collider could produce a world-ending black hole, he answered that calculations showed that this was incredibly unlikely, but that it was impossible to be certain: "the random nature of quantum physics means that there is always a minuscule, but nonzero, chance of anything occurring, including that the new collider could spit out man-eating dragons.' (Dennis Overbye, "Gauging a Collider's Odds of Creating a Black Hole", NYTimes, 4/15/08)

Quantum mechanics, causality, and objective reality

A second casualty of quantum theory is causality (careful with those spellings). Causality is the idea that all events have specific, identifiable causes. Because classical mechanics is deterministic, there is always an answer to the question "Why did I observe particle A at position X at time T?". Essentially, the answer is that given the initial conditions of particle A, it HAD to reach position X at time T. Of course, I may not know the initial conditions with certainty. In that case, I may only be able to estimate the probability of finding the particle at position X. But this uncertainty is extrinsic; it is due entirely to my lack of knowledge about the initial conditions. If I did know the initial conditions exactly, there would be no uncertainty at all in my prediction of the particle's future position. Furthermore, Newton's laws would specify a clear chain of causality between the particle's initial and final positions.

In contrast, causality in quantum mechanics is much harder to define, since quantum measurement is inherently probabilistic. The wavefunction of a particle does not specify the exact position and momentum of a particle, but only a distribution of possible positions and momenta that would be observed if the particle were measured. As a result, the answer to the question "Why did I observe particle A at position X at time T?" changes dramatically. There is no answer to that question given by quantum mechanics. Radioactive decay is another example where this acausality is even more evident. Let's say that I place a Geiger counter next to a single radioactive atom with a half-life of ten seconds. After 8.2 seconds the Geiger counter clicks, indicating that the particle has decayed. The question is, "why did the particle decay at 8.2 seconds and not 11.4 seconds or 14.1 seconds? What caused this event?" Again, quantum mechanics gives no answer. The lack of an answer is not due to a lack of knowledge about the initial state of the system, but to the inherent randomness of quantum mechanics. Even if I know absolutely everything there is to know about a particular quantum mechanical system, there will still be an inherent randomness in its measured properties.

This indeterminateness of quantum mechanics goes even deeper than causality. One of the common assumptions that we make about the universe as scientists is "objective realism". Objective realism is the idea that objects in the universe possess properties independent of measurement. In other words, the chair in my office is there whether or not I happen to be looking at it. The property called "position" can be thought of, in classical mechanics, as a little tag affixed to the chair. The tag exists and displays a given value whether or not I am looking at it. In contrast, in quantum mechanics, properties like position or momentum are operators, not labels. Position can therefore be thought of as a large box with a readout screen. I put my chair into that box, and the readout screen gives me a value which I call "position". Position is not "affixed" to the object; rather it is a value that I obtain through performing a specified action on an object.

Einstein himself was so disturbed by the indeterminateness of quantum mechanics that he never fully accepted the theory. In fact, to show that quantum mechanics was "incorrect, incomplete, or both" he proposed a thought experiment known as the EPR experiment designed to show the logical inconsistencies of quantum mechanics. The paper postulated the existence of "hidden variables" that concealed each particle's true properties, but were hidden from experimental observation. At the time, although the paper generated much discussion, most adherents of quantum theory did not accept its logic. Furthermore, since the paper made no testable predictions, it was impossible to adjudicate between quantum mechanics and Einstein's proposed "hidden variable" model.

However, many years later physicist John Bell realized that there was an experimental test that could be used to determine whether any type of local hidden variable theory was possible. In the last several decades numerous experiments have all shown the same answer: quantum mechanics wins. Physicists must jettison the concept of either realism (the idea that objects have properties independent of measurement) or locality (the idea that effects cannot propagate faster than the speed of light). Although some physicists who adopt a neorealist interpretation of quantum mechanics (see below) retain realism at the expense of locality, most modern physicists retain locality at the expense of realism.

If we follow most physicists in rejecting realism, the immediate consequence is that it is strictly meaningless to speak of objects as having properties independent of measurement. The statement "the chair is in my office" has no meaning. Instead, you can only say things like "I measured the position of the chair and observed that it was in my office". Lest you think I am exaggerating, let me recount a story that is told about Einstein by his biographer and fellow physicist Albert Pais. Pais recounts that once while they were out walking, Einstein turned to him and asked him "whether [he] really believed that the moon exists only when [he] look[s] at it". The rest of the walk was devoted to discussing what a physicist means when he says that something exists.

What are the philosophical implications of the indeterminacy of quantum mechanics? I believe the main implication is that reality is, in some ways, beyond the reach of human observers. Experimental systems in quantum mechanics are specified completely by their wavefunctions. Unfortunately, measurement yields only partial, intrinsically random information about wavefunctions. Unlike a classical universe in which every object carries with it a set of neatly ordered labels specifying its properties, quantum mechanics describes a universe in which objects present to us the merest glimpse of their nature while keeping their true reality hidden from view.

Quantum mechanics and consciousness

Another common, but by no means ubiquitous, assumption of a materialist worldview is that human consciousness or subjective human experience is an artifact of physical constituents. In other words, in opposition to a dualistic view which sees "mind" as separate from "matter", materialists usually argue that mind is merely a byproduct of matter which does not have an independent existence or a special, distinct role in the universe. Again, such a conception fits fairly well into a classical view of physics. After all, where does the "mind" reside? Is it some disembodied substance that floats inside the brain? If it has a separate existence apart from matter, how do the two interact? Shouldn't the interaction show up somewhere in our formulation of physics? Because classical physics required no appeal to some conception of consciousness, it was possible to jettison the idea of mind altogether. Again, quantum mechanics turned these ideas on their heads.

Consider the following statement by Wigner (a Nobel laureate and one of the founders of quantum mechanics): 'it follows that the being with a consciousness must have a different role in quantum mechanics than the inanimate object' or von Neumann (another Nobel laureate and founder of quantum mechanics): 'we must always divide the world into two parts, the one being the observed system, the other the observer' or Hugh Everett (who constructed the many-worlds interpretation of quantum mechanics), 'we are forced to admit that systems which contain observers are not subject to the same kind of quantum mechanical description as we admit for all other physical systems.' (Barrett, 1999). What on earth were these people talking about?

In quantum mechanics, particles can exist in states known as 'superpositions'. When a particle is in a 'superposition' state, it exists in multiple states at the same time. For instance, a classical coin is either in the state heads or tails. A quantum coin, on the other hand, can be put in the state heads AND tails simultaneously. Let's imagine that we put a quantum coin in such a heads-and-tails state and then measure the coin. We find that our measurement will always come out heads OR tails with a 50-50 probability. Furthermore, subsequent measurements of the same coin will find that it remains in whichever state we observed, either heads or tails. Somehow, our measurement of the coin has altered the state of the coin. Before the measurement, it was heads-and-tail, but afterwards it collapsed into either the state heads or the state tails. Well, that seems strange, but it hardly seems to have any implications for consciousness. Until we start thinking carefully.

When exactly did the coin go from being heads-and-tails to heads or tails? Well, perhaps that occurred when a photon from the lamp in my room first struck the coin. But actually, if we make careful measurements of the photon and the coin, we find that the photon doesn't cause the wavefunction to collapse (because we can reverse the action of the photon and the coin will go back to heads-and-tails). Well, maybe the first photon interacted with an atom in my retina, and that caused the wavefunction to collapse. But actually, if we make careful measurements of the photon and the coin and an atom, we find that the photon and the atom don't cause the wavefunction to collapse. We can keep going and going, pushing back the moment of collapse further and further, until we eventually hit a wall. That wall is the consciousness of the observer. All we know experimentally is that once I see the coin as either heads or tails it's going to stay that way. Can we test whether my mind actually causes the collapse? Unfortunately not (unless we can figure out how to literally stick my head into the measuring device). So evidence seems to indicate that wavefunction collapse occurs somewhere between the coin and my mind, but all of the intermediate steps that we can test seem to indicate that collapse doesn't happen at any lower level.

Is this an ironclad proof that mind is somehow distinct from matter in the universe? That depends on your interpretation. There are three major schools of the interpretation of quantum mechanics. The first is called neo-realism, and was supported by Einstein. Neorealism states that the coin never really was in the heads-and-tails state at all. Instead, it secretly was always in a single heads or tails state. However, the "true" state of the coin was hidden from us, fooling us into thinking that it was in a heads-and-tail state. This model avoids the problem of wavefunction collapse and consciousness, but it runs into serious difficulties and must invoke undetectable, faster-than-light pilot waves in order to explain modern experiments. Needless to say, few modern physicists support this view. The second interpretation is called the Copenhagen interpretation, and is generally viewed as the "orthodox" interpretation which is taught (vaguely) in most textbooks. The most consistent form of this interpretation (in my opinion) is that mind (maybe human, maybe otherwise) is indeed distinct from matter. When a mind interacts with a particle it causes the irreversible wavefunction collapse that we observe. Again, the role of consciousness is generally glossed over in most textbooks, but a consistent description of this position cannot really avoid it. Because most physicists are uncomfortable with such an explicitly dualistic view of reality, many now subscribe to the final major interpretation, the many-worlds hypothesis.

The many-worlds hypothesis has the advantages that it is mathematically simple and that it treats everything uniformly (there is no distinction between mind and matter). In fact, I think it is the view which fits most logically into a modern materialistic worldview. The many-worlds interpretation (which could more correctly be called the many-minds interpretation) states that whenever a measurement is made by a conscious observer, the universe splits. For instance, when I measure the heads-and-tails coin, the atoms in my brain enter the state "seeing-heads-and-tails". In one "universe" my brain tells me that the coin is heads and in the other "universe", the brain tells me that the coin is tails. The beauty of the many worlds interpretation is that it avoids any wavefunction collapse or problem with consciousness. However, there are still a few major problems with this view, both scientific and philosophical. Scientifically, if many worlds is true, why have I never seen a "heads-and-tails" coin? If the atoms in my brain are "really" in a superposition state of seeing both heads and tails, why do I only see one or the other? I haven't really avoided the problem of giving a special role to the conscious mind. The "mind" somehow can only see the one particular universe in which it exists, even though reality consists of a superposition of all these universes.

Philosophically, there are even bigger problems. If there really is this kind of multiverse, isn't science doomed? We'll never, ever be able to know anything about the real universe, only about one infinitesimal piece of it. Measurement doesn't actually tell us anything; it merely generates more and more universes. Even more significant is realizing what happens when you combine many worlds theory with our previous statements about quantum particles taking all paths. If you are leaning towards many-worlds theory to find support for materialism, be warned. Quantum mechanics states emphatically that anything CAN happen. Many-worlds theory goes one step further and says that everything DOES happen. At least quantum mechanics allows you to say that although miracles are possible, they are incredibly, incredibly unlikely. But many worlds theory says that no matter how remote the possibility, there is a universe in which any given event does happen. In fact, there are an infinite number of universes in which any given event happened. There is a universe in which I am the king of Elvisland. There is a universe in which I am forty-feet tall with machine guns for arms. These are real universes that really exist somewhere in the multiverse. Then how on earth do you know that you are not living in the universe in which Jesus walked on water? Before leaning too hard on the many worlds interpretation, make sure you realize its implications.

Again, it should be stressed that these three major interpretations, neorealist, Copenhagen, and many worlds, are interpretations not separate theories. All three are totally consistent with current observation and none of them as yet makes experimentally testable or falsifiable predictions which differ from the others. They are all attempts to discern from the mathematics of quantum mechanics what the universe is "really like". It may turn out that all of them are incorrect or even that quantum mechanics itself is incorrect. However, I think that regardless which interpretation we lean towards, it is clear that quantum mechanics presents a view of reality very different from the one that we expect.

Conclusion

So where do we stand? If quantum mechanics has turned our view of reality (even our definition of the word "reality") upside down, should we conclude that science is useless? That the universe is incomprehensible? I don't think so. But I think that quantum mechanics does show the danger of founding our core beliefs on our current understanding of modern science. Sometimes our understanding is correct, but sometimes it is not. I think it would have been quite a tragedy for some Christian in the 19th century to have abandoned the Biblical view of a sovereign God in favor of a distant clockmaker because he was persuaded by the overwhelming evidence of classical mechanics. If only he had lived a few more decades! For that matter, what will all my arguments mean if in ten years we discover that quantum mechanics is, after all, not the ultimate theory of reality? Think how foolish the science and philosophy of the ancient Greeks and the medieval alchemists look in the light of the 21st century. And have we now arrived at the summit of human knowledge? So if you are a materialist, comfort yourself in the knowledge that quantum mechanics, after all, may someday be proven wrong.

If nothing else, quantum mechanics teaches us humility with regard to our own knowledge. Our understanding will always be partial, mostly incomplete, and often faulty. Certainly, the Bible does not discuss quantum mechanics and the nature of measurement; if we want to learn about the laws of nature, science is the best tool that we have. But science, at its best, will lead us to ask questions that are beyond its reach. Is there a greater Law behind or above the natural laws that we observe? Is there a greater Reality behind the realities described by physics? In looking for answers to these questions, science cannot help us. If we want truths that go beyond the natural, we need to look to for a source beyond the natural. The Bible presents us with a God who is both transcendent and immanent, a God who is both infinitely beyond the created order and intimately involved with it, whose ways are not our ways and whose thoughts are beyond our understanding. If we want to understand the universe, the wisest thing we can do is first to seek the one who created it.

"Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make your paths straight" - Proverbs 3:5-6


Related essays:
If anyone reading this essay has questions about it or about Christianity in general, feel free to e-mail me at Neil -AT- Shenvi.org. I also highly recommend the book The Reason for God by Tim Keller. It is phenomenal. Free sermons treating many of the topics covered by this book can be found here.

Back to home Back to Essays